1. Field
Disclosed herein is a purification media comprising a rigid porous polymeric block having an exterior surface and an interior surface, and containing porous, polymeric fabricated to have a wall that is thin, and a pressure drop between the exterior surface and the interior surface that is low, when compared to conventional commercial carbon purification blocks. In particular embodiments, the rigid porous polymeric block is desirably coupled with an additional material disposed on the exterior or interior surface thereof and in particular with a nonwoven fabric containing, an active material, such as aluminum-containing fibers or particles. These aluminum-containing particles or fibers may be in the form of metallic aluminum, alumina, aluminosilicates, or combinations of these. The purification media is suitable for purifying fluids, such as water, thereby removing one or more contaminants from the fluid and for reducing scale formation in equipment in contact with such purified water.
2. Description of Related Art
Diarrhea due to water-borne pathogens in unsafe drinking water is a worldwide problem for many people, particularly in developing countries and emerging economies. While a number of different technologies are available for purifying water, most of these involve some form of mechanical filtration or size exclusion. Such techniques typically involve the use of submicron filters to remove pathogens. These filters, in turn, require elevated water pressure, particularly for point-of-use (POU) water filters, where clean water is expected to flow from a supply source within seconds of being turned on.
Various purification media have been proposed that use blocks of activated carbon particles, zeolites, metal oxides, and other materials. Often, these materials purify fluids by one or more mechanisms, including size exclusion, physical entrapment, or chemical reaction of the contaminants. The latter two mechanisms generally require some physical interaction between the active purification elements (e.g., carbon particles) within the purification media and the contaminant-containing fluid to be purified.
The particles of active purification elements may be dispersed within, or agglomerated by, a binder of some sort, typically a polymeric binder. The design of these media is complex and difficult, typically requiring trade-offs between properties such as the activity of the filtration media in removing contaminants and the pressure drop of fluid across the purification media. For example, decreasing the average particle size of particles in the purification media may increase their activity in removing contaminants by increasing the specific surface area of the particles that is exposed to contaminant-containing fluid. However, such an approach may result in increased pressure drops across the purification media, which actually decreases the flow rate of fluid that may be purified using the purification media. This can lead to the need for multiple filtration systems in order to purify a commercially acceptable amount of fluid. Other design problems include balancing the need for structural integrity of the purification media under fluid pressure with the need for fluid to be able to penetrate the purification media and come into contact with the active purification elements therein.
The need to reduce pressure drop across the purification media is particularly acute in filtration systems that are to be used in developing countries and/or countries with emerging economies. Such systems are often used where the available water pressure is extremely low, typically only a fraction of the water pressure that is generally available in developed countries. For example, municipal water pressure in Mexico City is generally 14-16 psi. Water pressure in Mumbai is generally 12-16 psi. The availability of a low pressure drop purification media would allow for water purification at available water pressures in developing countries without the need to use additional energy pumping the water to a pressure that is generally available in developed countries.
For example, water purification media for use in refrigeration systems, such as residential and commercial refrigerators and freezers containing water lines, ice makers, and the like, generally require purification media that are capable of processing large amounts of water over a significant period of time without the need to change the filter frequently. A relatively low pressure drop in such systems is desirable in emerging economies because of the low water pressure generally available in such countries.
For example in a commercial point of use water purification in the U.S., the available water pressure is typically around 60 psi. However, purification media designed for use under such pressures would not provide adequate water flow in, e.g., Brazil, where the typically available water pressure is from 7-15 psi. Similarly, a purification media that is designed to require a water pressure of 60 psi to produce adequate flow would be unsuitable for use in a water line in a refrigerator in these countries, because water at a much lower pressure is generally all that is available.
At least part of the reason for the inability of conventional water purification systems to operate effectively under low water pressure conditions is the higher design pressure drop noted above. However, this high pressure drop is not simply a function of the design parameters of conventional purification media, but is a function of the particular active purification materials used therein. For example, purification media containing activated carbon derived from coal and the like according to conventional methods and used in conventionally designed purification media would yield a purification media that provides little or no water flow at a water pressure of 10 psi. In this regard, conventional purification media that are designed to remove bacteria from water and are rated at 0.2 micron will not provide adequate flow (if any) at a inlet pressure of 10 psi.
Another reason for the lack of effectiveness of conventional carbon block filters in emerging economies is the high water turbidity often encountered there. This can be due to a number of factors, and may be associated with the presence of pathogens or other contaminants in the water which should be removed to render it safer.
While a combination of a pleated filter element and a carbon block filter has been proposed in U.S. Patent Application Publication No. 2004/0206682. However, the arrangement suggested therein places the pleated filter element around the outer surface of the carbon block filter, so that incoming water encounters the pleated filter block prior to encountering the carbon block filter. Such an arrangement results in clogging and/or exhaustion of the pleated filter with contaminants, resulting in insufficient water flow through the filtration system.
While not wishing to be bound by theory, it is believe that an alternative to impaction and sieving is electrokinetic adsorption, where the media is charged and particles opposite to that charge are attracted and adsorbed. Membranes have been modified to provide some electropositive functionality, but none appear to be suitable for low pressure operating.
Examples of such materials are disclosed in U.S. Pat. Nos. 6,838,005; 7,311,752; 7,390,343; and 7,601,262. These materials, when used as water filtration media, have been found by the present inventions to be unsuitable for low pressure use, despite any suggestions to the contrary in the above cited documents. The present inventors have found that, even at low input pressures, the materials are subject to unsuitable amounts of compression and distortion, so that they are ineffective for practical use. In addition, the solution to this problem suggested by the patentees (placing multiple layers of the fabric in series) results in a significant pressure drop (e.g., 80% of incoming water pressure), making the material unsuitable for a low pressure installation. In addition, the extra layers of nonwoven fabric substantially increase the cost of this proposed solution. The nonwoven fabrics are disclosed to contain nanoalumina fibers.
Attempts to use microbiological interception filters are described in U.S. Pat. Nos. 6,913,154 and 6,959,820. However, these attempts use a so-called silver-cationic material-halide complex. Such a complex is difficult and expensive to prepare and use.
Another problem typically occurring in water supply systems and in circulating water systems relates to the formulation of mineral scale. Dissolved solids in the water can precipitate onto surfaces of water processing equipment, interfering with the operation of such equipment. For example, heat exchange surfaces in contact with water having mineral solids dissolved therein can become fouled as mineral scale deposits thereon, interfering with the designed heat transfer characteristics of the surface, and rendering a heat exchanger containing such a surface less efficient. Mechanical filtration is of limited usefulness in addressing such problems, as the main cause of scale is typically solids dissolved in the water, rather than suspended solid particles.
Accordingly, there remains a need in the art for a purification media that can provide purification of fluids, such as water, by removing significant quantities of contaminants while the purification system is processing water at significant flow rates with a low pressure drop across the purification media. Such a system must be able to process large quantities of water without clogging or substantially increasing in pressure drop.
Similarly, there remains a need for a water purification system that reduces or eliminates scale formation in equipment used to process water, including water supplied at low input pressures.
In addition to the need for filters that function at low water pressures, there is a need for purification systems that are sufficiently small that they can be incorporated into the water supply lines in household appliances, such as refrigerators, dishwashers, laundry washers, and the like.